Powder metallurgy and piston rings obtained thereby



','PoWDER `1vinra-trunurAND PlsToN Y T ne l script'inthereof.

onrAnsEn rHEREBY y Max Koehler, *Witten-Bommern, Germany, assigner to I' -K a August H.' Schilling, Atherton, Calif.

l l No Drawing.k Originalrapplication'December 22, 1950,

ASerial No.l202,395, now 'PatentrNoL 2,741,827, dated *I pril 17, 1956. Divided and this application April 2,

` q 11956, serial No. 575,637

l 11 claims. Y(c1. '14s-412) ,The ypresent'invention relates to the m'anufact'ure V of Y piston rings `for' vhigh speedy internal combustion engines j. based upon the pressing and sintering of mixtures of j metallic powders, the main ingredient ofy whichfis lpow-V 1 dered iron, `:andjcontaining minor proportions *ofV pow'- f d ered 'leadjandr'graphite.' 'j j l t Y The present application isa division of my copending RINGS Y fatent Oiiice l application SerialNo. 202,395, iledDecember 22 1950, Y

now latentA No.1 2,741,827, granted April 17, 195.6.

t. "iin the known production ofwobjects, for example, piston rings, by the powder metallurgical process.,` theA metal 'powder is'usually subjectedto a pressing 'with-'a v'subsequent sintering, vthat isgajheat -treatment'fyi/herein the temperature lies Vconsiderably under 'the meltingv point` ofthe ypowdered metal mixture;r In type of manu# v facture', it is well known that Y'the strengthof v`thevfthusV f, produced s'intered'body can be increased by the addition of small percentages of manganesegchromiumfor silicon p Vtovgthe soft iron powder. It has pals'ob'een attempted "to j A increa'sethe strengthY of the resultant material by cold'-Y f pressing the san-1e'subsequenttothe-sintering or by 4sub,- "j'ecytingit to' several sintering treatments., No noteworthy increase in Ythe materialV strengthhas; howeverbeen i v:attained by these processes.V Q Y i lltiis also known that objects may'b'emade'from mixturesl ofy powderedfmetals when thepressing and sinteringv yprocesses arel combined into a single 'process of hot-press? VExperience has shown, however, that piston rings `manu'- V"factured according to the above suggestions `are not entirely satisfactory for use in high' speedinternal'combusy' [tion engines,y for thelatter impose very high thermal and mechanical 'stresses-'upon the rings.

' ItzisthV gen ral object of the present inventiontoprovideanl improved' process 'forthe' manufacture of` piston Y rings and. other parts for use in enginesoperating at high improved process' for the manufacturetof piston ring materiallgby powder metallurgy wherein a mixture con- Qtaining from' 1% toj10'% of lead `with or without other ,1."heavy`metal's', and silicon components '.fallin. powdered `condition'in admixture with powdered iron and a'srnallV jfiproportion of powdered graphite, is-,convevrted y.irrtoail l extremely 'strong and j heat resistant body, having. excepY l bearing qualities, by sintei'ingandprlessing, Vandfi ranular pearlitic or 'sgorbitic-,st h objects and advantages'fof,y

j manner thattthematerial is givemadamellanpearli c The lamellar'pe'arlitic structure attained when, inlthe briquetted or preliminarily pressed to approximately the desired nal shape after mixing with a small proportion of powderedgraphiteand vwith from 1% to 10% ot pow-i dered lead whichmay bereplaced in part vwith *one or transition or transformation temperature, but Vno higherv Vthan theV sintering temperature, after whichit is either f 'rapidly quenched, where the material is totbe subjected in use totemperatures up to about 300 C., under load, or is allowed to cool slowly Where it is to be subjected f to maximum'temperatures of about'200 C. under load.

When additionsof theheavy metals, suchtas tin, anti.-

mony, 'manganese chromium, nickel and copper,V and o also of silicon, are used along with the lead, kthe 'ratio of the additions to the quantity of klead mustbe so regulated that the diffusion processes internaltothe mixed crystalline series structure, like Fe--Pb-'Sm Fe-,Pb-Si, and Fe-lb-'Sb-Si, are prevented. 'Y y My improved process'may be varied in v for controllingl thepr'opertiesofthe nal product. In one modification of'fmy process, itis soughtfto obtain Va granular pearlitic `*or tsorbiticr structure Ywhiclrisvp'ar'.-

ticularly desirable for pis'tonringssubject to highther` i mal stress in high-load, high-'speedinternal .combustion engines, for example, those in which the operating piston j f ring temperature reaches approximately 300" C; 'Inga modified procedure, it is desired'to attain a tine lamellar pearlitic Ystructure whichis particularly desirable forthe V; l pistonfrings'of high speed internal combustion-engines which are operated at a thermally lower-stress,7 where the ring Y Y temperatures 'do notV Vexceed approximately zoceC.

production of'the piston ring material, iron powder vcontaining a 'small proportion Vof graphiteiis mixed with a heavy metal powder consistingentirely or preponderantly oflead, with or without silicon, inthe limits of 1` to`10`%,

preferably about 5%, which mixture is rstvpressedto a specic gravity of approximately.6.3 to 6.5 andfthe briquette is` then sintered for fromY one to two hours at 1000 to 1200 C. lfollowed by a step-wise coldpressingY to a nal pressure of about 140,000 lbsL/in.2 kg./cm.2) kto `a speciic weight of 7.6 to 7.7 and with a iinal heating to 850'to 900C. for approximately one hour, followed by a slow cooling. This lamellar pearlitic structureis particularly desirable for piston rings for high speedtinternal combustion engines operating under thermal stresses'of the order of -app'roxima'ttely- 200 For piston rings for high speed internal'combustion v engines with thermally more highly stressed'V rings, Vfor example, where the piston ring-operating temperatureis a specific gravityfoi 6,3 to 6.5-, rthen `sinteredforgone to two hoursat 1000,o i;tof1200 C.V andyto obtaina materialVV f f with a granular;pearlitic structure, the briquetting and A sintering arefollovgved, byjfa 'step-wise"coldpressing tok Vabout 140,000 lbs./in.?jbyl which ati/specific g'A vityV 'of Y V7.6 to 7.7 is obtained; jAftejr a subsezijnefit'heattreatrv Y ment at s5crto9oo C. fofapprsntaately me hour, a f rapidquenching is carried out, tor'yexamplepin oil.l Y

, t V2.842.471, gPatented July Y 8,A

several `waysA i This last described process can be altered in that the cold-pressing occurs in stages up to pressures of about 210,000 lbs/in.2 (15,000 lig/cm?) and that after a rapid quenching from approximately 760-to 820, for example, 800 C., a further soaking occursat a temperature from 500 to 650 C., or at any temperatures lying under the transition point cfapproximately720 C. ln further explanation, the following maybe noted:

During the cold-pressing, the cementite as well as the free graphite still present, and the mixed crystals of the Fe--C-heavy metal group, which were formed by the sintering subsequent to the briquetting, are distributed. In consequence, a rapid conversion into martensite is Obtained by the subsequent heating to 760 to 820 C. with the rapid quenching that follows. With the subsequent soaking at temperatures of approximately 650 C., a grain structure build-up results whose special characteristic is annealed so-rbite. This gives to the material the characteristics which are valuable for piston rings; namely, a. higher elastic limit, strength and a springiness as well as extremely good running and slipping characteristics as yet not attained oy any other process. The length of time required by the soaking must be deter- `mined `by the cross section of the material and the desired strength; the time increases with larger cross sections and for the reaching of higher strengths.

'The following example will serve to illustrate the invention more specifically without, however, indicating the limits thereof.

Y Example The following materials were mixed together:

. Percent -Powderedliron (with impurities of 1%) 94 Powdered graphite (ash content .Powdered lead with additives 4.5

which mixture had the following approximate grain size distribution:

Percent Under 0.06 mm -Between 0.06 and 0.1 `mm 39 `Between 0.4iand 0.2 mm. 26

Over 0.2 mm

The initial pressing or briquetting of this material 'occurred at apressure of about 70,000 lbs/in.2 (4,900

'kg/cm?) followed by sintering at approximately 1100D `C. for two hours in a neutral furnace atmosphere.

This Vcrude sintered mass hada porosity of approximately 23% land an ultimate strength of 14,000 to 17,000 lbs/in.2

`(10 to l2 kg./mm.2).

After sintering, the mass was cold-pressed in stages Vuntil a maximum pressure of about 140,000 lbs/in.2

=(9'800 lig/cm?) was reached. This material was subsequently heated and held for one hour at a temperature of 850 C. (The effect attained'by this heating may be `developed in a shorter time by the use of a higher ternperature, which temperature, however, may not exceed lthe sintering temperature.) At the end of this annealing, the material was oil-quenched and soaked at a temperature of 650 C. Examination showed it had a `definite grainy pearlitic structure, and the characteristics (approx. 94.7%

While in the foregoing, IV have referred specifically to iron as the ferrous component, it will be understood that various suitable types of steel can be employed, in place of various forms of iron, suitable adjustment of the quantity of graphite being made where necessary.

The term heavy metal or heavy metal powder as employed in the specification and claims is to be understood as having reference to a solid metal of an atomic weight above 50 and of the type commonly employed in the metallurgy of iron and steel, and in minor proportions with reference to the iron, in order to modify the properties of the essentially ferrous product. The lead, tin, antimony, manganese, chromium, nickel, and copper referred to hereinabove are typical examples of additions in modified iron and steel products and ferrous alloys.

l claim:

1. Processfor the manufacture of pistonrings suitable for use in high speed internal combustion engines, the steps which comprisepressing a mixture of a preponderating proportion of iron powder, about 1 to 10% of lead powder, and a smallV proportion of powdered graphite to Iapproximately the desired shape, sintering the mass, subsequently cold-pressing the same, and thereafter reheatingthe pressed mass.

2. Process according to claim 1, wherein the sintering takes place at a temperature of about 1000 to l200 C. for about one to two hours.

3. VProcess according to claim 1, wherein the mass is slowly cooled'after the reheating.

4. Process according to claim 1, wherein the mass is quenched after the reheating.

5. Process according to claim 4, wherein the sintering takes place at a temperature of about 1000 to 1200 C. for about one to two hours, and wherein the reheating occurs to a Vtemperature above the transformation temperature, but no higher than the sintering temperature.

6. Process for the manufacture of piston rings suitable for use in high speed internal combustion engines, the steps which comprise pressing a mixture of a preponderating proportion of iron powder, about 1 to 10% of lead powder, and a small proportion of powdered graphite to a specic gravity of 6.3 to 6.5, sintering the mass at a temperature of about 1000 to 1200 -C. for about one to two hours, subsequently cold-pressing the mass in stages at pressures up to about 140,000 lbs/in.2 to a specific gravity of 7.6 to 7.7, reheatiug the mass to a temperature above the transformation point but .below the sintering temperature, and then rapidly quenching it.

7. Process for the manufacture of piston rings suitable for use in high speed internal combustion engines, the steps which comprise pressing a mixture of a preponderating proportion of iron powder, about 1% to 10% of lead powder, and a small proportion of powdered graphite to a specific gravity of 6.3 to 6.5, sintcring the mass at a temperature of about 1000 to 1200 C. for about one to two hours, subsequently cold-pressing the mass in stages at pressures up to about 210,000 lbs/in?, reheating the mass to a temperature above the transformation point but no higher than the sintering temperature, rapidly quenching the mass, and then annealing the mass at a temperature below the transformation point.

8. In a process for the manufacture of piston rings Vsuitable for use in high speed internal combustion engines, the steps which comprise mixing a preponderating proportion ofviron powder with about 1% to 10% of 'powdered lea'd 'and a small proportion of powdered graphite, pressing the mixture to a specific gravity of approximately 6:3 to 6.5, sintering the shaped mass at about 1000 1:01200" C. foriaboutone to two hours, subjecting the mass to ya stage-wise cold-pressing at pressures up to about 140,000 lbs/in.2 to 'a specific gravity of 7.6 to 7.7thereafter heating the mass for approximately one `hour at about850 to'900 C., and then rapidly quench- ,ing the same.

9. Process according to claim 1, wherein the mass is f n quenched after the reheatingg and then is soaked at a References Cited in the file of this patent temperature below the transformationpoint. i l n L v j 10. Process according to claim 6, wherein the mass, f UNITED STA-@ES PATENTS* after the quenching, is soakedat` a temperature of about 2,491,238Y Whitneyr Dec. 13; l19749 11; Process according to claim 8, wherein the mass, 

1. PROCESS FOR THE MANUFACTURE OF PISTON RINGS SUITABLE FOR USE IN HIGH SPEED INTERNAL COMBUSTION ENGINES, THE STEPS WHICH COMPRISE PRESSING A MIXTURE OF A PREPONDERATING PROPORTION OF IRON POWDER, ABOUT 1 TO 10% OF LEAD POWDER, AND A SMALL PROPORTION OF POWDERED GRAPHITE TO APPROXIMATELY THE DESIRED SHAPE, SINTERING THE MASS, SUBSEQUENTLY COLD-PRESSING THE SAME, AND THEREAFTER REHEATING THE PRESSED MASS. 